Carbon dots as dual-action nanotools for metal toxicity recognition and mitigation

Carbon dots (CDs) have emerged as promising agents for mitigating metal toxicity and monitoring metal contamination in aquatic environments. This study investigated the dual functionality of CDs as anti-toxicity agents and biosensors for cadmium (Cd²⁺), nickel (Ni²⁺), and silver (Ag⁺) in a zebrafish embryo model. Zebrafish embryos were exposed to various concentrations of CDs (0, 5, and 50 mg L^-1) in combination with different metal concentrations. Toxicity was assessed by measuring the lethality, hatching rate, swimming activity, and AChE activity. CDs significantly reduced the lethal toxicity of all tested metals, with LC₅₀ values increasing from 56.0 to 110.0 μM for Cd²⁺, 0.4-1.6 μM for Ag⁺, and becoming undeterminable for Ni²⁺ at the highest CDs concentration. Photophysical characterization revealed that the CDs exhibited metal-specific fluorescence, enabling the development of an optical fingerprint for metal identification. Fluorescence imaging of zebrafish embryos demonstrated the effectiveness of CDs as in vivo tracers of metallic contaminants, highlighting their utility in studying biological processes. These findings highlight the dual functionality of CDs as agents to reduce metal toxicity and as monitoring tools for water quality assessment, making them a versatile solution for addressing metal contamination challenges in aquatic and biological systems. ENVIRONMENTAL IMPLICATIONS: The present study explores the potential of carbon dots as nanotools for water remediation. Carbon dots have a high absorption capacity and can remove several compounds, including metals, from aquatic environments. This is highly relevant because contamination by metallic compounds is an environmental concern and that technology is constantly being sought to minimize the impact of these compounds on aquatic systems. Due to natural fluorescence which can be changed by metallic ions, carbon dots also show potential for monitoring aquatic contamination contributing as a potential tool in risk assessment strategies.